Generally, the invention of the application provides a method and a means, utilizing an aqueous froth, for filtering an air stream. More specifically, the invention provides a method of removing volatile or inert gaseous, liquid, and solid contaminants from an air stream. The invention also provides a liquid-bath, froth-filtered, saturated-fiber air filter device for removing contaminants from an air stream. The invention is also effective in removing abraded drywall joint compound dust from an air stream.
Nuisance dust is any particulate that is micron/sub-micron in size, and small enough to pass through dry air filter elements. Nuisance dust is generated by natural and artificial means. Examples of natural dust include wind-blown sediments and evaporates, pollen, microscopic organic detritus, allergens, and ash from fires and volcanic eruptions. Artificially caused dust includes acid rain, industrial emissions, vehicle exhaust, mining and construction processes, man-made fires, inadequate soil management, paint, fertilizer, and other chemical sprays.
The prior art includes the Dular U.S. Pat. No. 6,083,307 dated Jul. 4, 2000, which teaches an apparatus for separating sanded drywall joint compound from an air stream. Dular does not teach the use of an aqueous froth and does not teach the use of radially extending filters that cooperate with the aqueous froth.
The prior art also includes the Driker et al U.S. Pat. No. 5,820,657 dated Oct. 13, 1998, which teaches a percolating vacuum system. Driker et al is concerned primarily with uninterrupted conversion from wet-to-dry or dry-to-wet vacuuming, which requires the use of a cumbersome deflector and float mechanism. The present invention avoids the deflector and float apparatus of Driker et al. Furthermore, the present invention provides additional filtering stages using wetted fiber filters that cooperate with and enhance the aqueous froth filtration.
The prior art includes dry filter methods for improving micron/sub-micron sized particulate filtration as disclosed in Busch, U.S. Pat. No. 4,116,648.
The prior art also uses water as a micron/sub-micron filter media. Water reservoirs, cascades, sprays, and cyclones are incorporated in air scrubbing devices large and small as shown in Napadow U.S. Pat. No. 4,484,513.
The Wisting U.S. Pat. No. 3,989,484 teaches a cyclone-type air scrubber and filters with a liquid reservoir by introducing the contaminated air stream either above or below the surface of the liquid reservoir.
Yarbrough U.S. Pat. No. 5,428,865 projects particulate onto a water surface in an air chamber, but all the contaminate is not exposed to filtering surfaces, leaving unfiltered contaminate in the air stream.
Blair U.S. Pat. No. 5,669,946 uses plastic members to increase water surface. Blair recognized the need to increase the water-surface filter area. However, mechanical members limit the filtering surfaces to a predetermined area, take up space in the waste receptacle, and add to manufacturing cost.
Another prior art approach introduces the contaminated air stream below the surface of a water reservoir. Mechanical circulators, baffles, and collectors channel the contaminated air stream into a circuitous path, exposing the contaminant to the surfaces of the container, collecting the liquid and returning it to the reservoir. The baffles, circulators and collectors add extra parts to the device, raising manufacturing costs and reducing reliability.
For example, Scarp U.S. Pat. No. 5,199,963 teaches cyclone-type, mechanical ring baffles and fluid collecting rings to channel air into a circuitous path to collect and return water to a reservoir.
Aqueous froths are used in the prior art as a flotation means, usually to float mineral fines out of a slurry, and transport the fines to a containment vat where they are removed from the froth by various de-watering methods, as disclosed by Barwise U.S. Pat. No. 4,956,077.
During the process of finishing drywall, sanding joint compound generates nuisance dust that is difficult to contain and clean up. This nuisance dust is approximately 300 times smaller than the diameter of a human hair and readily passes through standard vacuum-cleaner filtering elements. Cleaning up the dust is costly and often extensive masking is required to prevent the dust, generated by the sanding process, from contaminating restricted areas. Such specific applications require an effective, efficient means for removing sub-micron contaminate from a vacuum air stream. Working in dust restricted areas, such as occupied homes, hospitals, computer centers, restaurants, office buildings, retail stores, art galleries, and hotels, where dust contamination is unacceptable, requires a more efficient solution.
It is applicant""s objective to provide an effective method and means of removing micron/sub-micron contaminants from an air stream, that is easy to clean, economical to manufacture and use, and durable and dependable enough for professional service. The present invention performs well in dust-restricted areas.
The dynamic interface between a contaminated air stream and an aqueous solution is exploited in one form of the invention to generate an aqueous froth with an exponential number of filtering surfaces. Turbulence generated in the aqueous solution, by the dynamic interface, is utilized to continuously saturate a fiber element. The saturated-fiber element establishes the upper boundary of the froth filter and adds a plurality of wet fiber surfaces providing an additional filtering stage to remove the contaminate not removed by the aqueous froth. The effects of gravity are exploited: adding to the momentum of the contaminate toward the bottom of the aqueous solution; to contain the dynamic froth environment in the scrubbing chamber; and to settle the contaminate out of solution, by alluvial sedimentary process. Another form of the invention generates the aqueous froth with clean air from a secondary source.
The aqueous froth is generated by exhausting a contaminated air stream through a diffusing sieve into a water column and exposing the contaminate to the inside and outside surfaces of the plurality of bubbles generated in the liquid reservoir. The air stream and any remaining contaminate are then exposed to a continuously saturated fiber element, exposing the contaminate to the plurality of the wet fibers of the element.
Contact between the contaminants in the air stream and the liquid surfaces of the aqueous froth is the primary means of transfer of contaminants from the air stream to the aqueous solution. Water is cost effective and widely available, replaced every time the filter is cleaned. There is no cost beyond the initial purchase of the filter.
Designed for easy cleaning, the air filter reduces the volume of unconsolidated contaminate to a volume consistent with an alluvial sedimentary deposit of clay. The cover assembly of the water reservoir container is removed and the sludge is hosed out of the container. The operator removes the pipe/fiber-element assembly from the fiber-element container and hoses the fiber elements until the water runs clear. The water reservoir container is filled to a predetermined level, the water reservoir cover assembly and the pipe/fiber-element assembly are replaced and the filter is ready for use.
The air filter has no moving parts, air and water are the only moving elements. All components are suitable polymeric compositions. The selected polymers constitute a durable filtration device that will provide years of economical, dependable service. The air filter of the present invention may be used as a pre-filter, in a condition of partial vacuum. The contaminated air stream is drawn by means of low pressure through the filter, discharging the decontaminated air stream into the vacuum hose toward the vacuum source.
The filter may be used as an exhaust filter in a condition of positive pressure. The contaminated air stream is urged through the filter by relative high pressure of the air stream, exhausting the decontaminated air stream into the atmosphere.
Additives to the liquid reservoir can increase surface tension, to increase froth duration and improve filtration; to act as a solvent, to remove contaminants from the air stream that are not water soluble; to act as a base, to neutralize acid contaminants; and to act as an pathogen, to sterilize organic-allergen contaminants.
The contaminated air stream is drawn through the aqueous solution by means of partial vacuum and into contact with the aqueous surfaces of the froth in the scrubbing chamber. Simultaneously, the turbulence generated by the interface continuously saturates a fiber element positioned a predetermined distance above the water surface. The saturated-fiber element effectively contains the expansion of the aqueous-froth filter. The air stream is drawn into contact with the saturated fiber element removing any remaining contaminate. Excess water rinses the contaminant from the fibers, back into the liquid reservoir continuously. The air stream is optionally drawn through a secondary fine fiber element, and returned to the vacuum line toward the vacuum source.
Other objects and advantages of the invention will become apparent from the following detailed description and drawings.